Gardening: Thorny solutions

Cats are the scourge of the urban garden: they view gravel paths and lawns as giant litter trays and flatten your favourite flowers. The best line of defence, advises Sarah Raven, is a selection of prickly plants

CATS CAN turn your whole garden into a problem area. They leave the nastiest things in the most irritating places: on your lawn, in freshly dug flower beds, or where you've just sown a perfect line of seed. There will be gaping holes in the turf to remind you that they were here yesterday and the day before that. But that's not all; where there aren't holes in your lawn, you'll have brown patches where their pee has scorched the grass, and they'll spray your lettuces too. They will fall asleep on your catmint, flattening the lot, and lacerate the bark at the base of your finest trees. Cats may treat your garden as if they own it, so what on earth can you do about it?

The best (and most selfish) cat deterrent is to have your own. When I lived in London my lawn was devastated by neighbouring cats until I got a couple of kittens. From the moment they were old enough, they were off into other people's gardens, preferring to use theirs as a loo, not mine. They're clean animals and as long as they belong to you, they will see off any cat which is considering using your garden as the local drop zone. Cats are nimbys.

If you can't bear the idea of getting a cat, then there are other options. You can use repellent substances, such as pepper dust, naphthalene, or aluminium ammonium sulphate liquids and powders, all available from vets. These can be sprinkled over the worst-affected areas. Their effect is short-term though, and the cats will return. Most of them have been designed to stop cats peeing in a particular place in the house, and are not really for use outside.

Alternatively, you could try an anti-cat alarm. These give off ultrasonic sounds that are virtually inaudible to humans, but sound painfully loud to cats, encouraging them to go elsewhere. In my experience, the effect of these is also short-term. Cats eithers seem to get used to the noise, or decide to turn a deaf ear. In less than a month, you are back where you started.

The most permanent solution is to avoid giving cats what they like. Gravel paths are a real favourite: they think they've found a giant litter tray. They also like loose, dry soil, or mulch-covered flower beds, which have more exposed soil than plant-cover; and a lawn with catmint edge is pure paradise. They can defecate and then have half an hour basking in the sun, lounging on top of your battered plants.

What they don't like is closely-planted gardens, with bold blocks of spiky plants. You don't have to turn your garden into a fortress - cats shouldn't require too much encouragement to seek a softer, less aggressive patch. Find out where the cats tend to be entering your garden and concentrate your plant tactics there, or use prickly plants as barriers around edges and borders. If you create ranks of lethal spears the cats are bound to move off to a less hostile plot next door. Luckily spikes can look fantastic, so your garden will be chic as well.

For ground-cover spikes, go for the thistle-like plant, Silybum marianum. This is a biennial that makes huge carpeting rosettes of shiny cream and green leaves over a metre across. They are handsome plants, with a halo of spikes around each leaf that makes them ideal cat deterrents.

Onopordum acanthium is another spectacular biennial which serves a similar role. Its ground-covering rosettes are bright silver, reaching about the same size across as the silybum, but each individual spike around the leaf edge is over an inch long and it has needles all over the stem as well. By mid-summer this Scotch Thistle is covered in purple flowers, towering six to eight foot high. A row of these will effectively act as a fence of barbed wire, and the plants will still provide ground cover cat protection from late summer to late spring.

Eryngium giganteum `Miss Wilmott's Ghost' would also be ideal, but they are only effective cat-repellants when in flower. The shield-shaped leaves are smooth and innocent, but the spiky flowers are far from it. They flower in early summer and look marvellous as they turn brown and dry out in the autumn. You can leave them in place as a sculptural presence right through the winter.

All three of these thistle-like plants are biennial. You can sow them now either direct into the ground, or into pots on the windowsill. They will germinate in a couple of weeks and should be planted out in groups of three or five, placed about a metre apart. In spite of the spikes, both silybum and onopordum tend to get eaten badly by slugs when they are young and will need protection. All three plants flower and set seed in the summer so once you've introduced them, they will scatter themselves all over the garden for ever more.

The last family of plants worth mentioning are the impressive-looking phormiums. The long, sword-shaped leaves form architectural tussocks that any cat will stay well clear of. They are evergreen, providing a dramatic backdrop to other plants in the spring and summer, and some much-needed structure in the lean winter months. They are not fully hardy, but seem to survive our increasingly warm winter months without the protection of a south- facing wall. With these four plants in your armoury, your garden should become a cat-free zone.

+ Late spring and early-summer flowering Ceanothus, like the evergreen C concha will be over by now, so it is the perfect time to prune. Don't do anything too drastic. Cut out any dead or diseased wood and then just clip it back to fit its space.

+ So you have a problem with docks? I do and am reluctant to use endless doses of glyphosate to sort them out. You will eventually exhaust them if you keep cutting them down at this time of year. They have put all their energy into producing flower spikes and are at full height by now. If you get in there just before the flowers open and die and seeds get scattered all over the garden, you should weaken the plant enough in a couple of years to kill it. This is the basis of the old rhyme "Cut your weeds in May, they're here to stay. Cut them in June, you're a month too soon. Cut them in July and they will die.'

+ Don't pour lots of grass clippings into your compost heap without a layer of straw between this weeks and those you added before. The grass clippings are too rich in Nitrogen and will rot down anaerobicly. If you add equal parts of straw to the grass, you add carbon and create the right balance for quick aerobic decomposition. If you turn the pile every week, you will have a mountain of your own perfect compost to use as a mulch all around the garden with 2 or 3 months.

ENDS - EA

RJC-PA

This week

1 It is time to prune late-spring and early-summer flowering Ceanothus. Don't do anything drastic: cut out any dead or diseased wood and clip it back to fit its space

1 Don't resort to glyphosate to sort your docks out. Cut them down now, just before the flowers open, die and set seed, and you should weaken the plant enough to kill it within a couple of years. This is the basis of the old rhyme "Cut your weeds in May, they're here to stay. Cut them in June, you're a month too soon. Cut them in July and they will die"

1 Add a layer of straw to your compost heap before adding more grass clippings. Equal parts of straw and grass are needed to create the right balance for quick aerobic decomposition. Turn the pile every week, and you will have a mountain of perfect compost within two or three months